1. Field of the Invention
The invention relates to a power screwdriver having a torque or rotating angle sensing element associated with the output shaft.
2. Background
Power screwdrivers are known such as described in German Patent Specifications DE-AS 24 23 300 and DE-OS 31 27 753, which exhibit right-angle gear units as an output or downline spur gear units including transducers which serve to measure the torque and/or the rotation angle during driving. As soon as the required rotation angle and/or the required torque is obtained, the measuring/control electronics generates a signal, usually a cutoff signal, with the result that the driving operation is terminated.
In the known power screwdrivers, the transducers and the transmitter are provided in the area of the drive shaft. Consequently, for example, a torque which is applied to a screw can be measured only indirectly. This is because the right-angle gear unit of the spur gear unit is situated between the bit, which is in engagement with the screw, and the drive shaft. Such speed-transforming gear units and above all the occurring friction and the associated inefficiency of the gear unit adversely affect the measuring accuracy. In the case of safety-type screw connections, the screws are tightened to their yield point. However, when the yield point is reached, the power screwdriver must reliably switch off so that the screw is not inadmissibly strained. With the known power screwdrivers in which the transducers are disposed in the area of the drive or on the drive shaft, this requirement cannot be met.
The object of the invention is to provide a power screwdriver of the initially mentioned kind such that the transducers for the torque and/or rotation angle can be disposed without increasing the overall dimensions of the power screwdriver housing in such a way that the influence of the gear unit and the friction are eliminated during measuring.